Providing a product which can be easily torn by hand but retains enough tensile strength to prevent undesirable tearing is typically achieved through perforations. Perforations are traditionally created by a mechanical cutter, consisting of a number of sharpened points spaced apart by depressions. As the cutter comes in contact with the material, the points create small holes. Where a depression makes contact, the material is left intact. This sequence of spaced-apart holes creates a material that under normal circumstances will remain intact but will tear when a certain amount of force is applied. The amount of force needed to tear the material will depend on the type of material, as well as the size and spacing of the holes. The size and the spacing of the holes may be varied by changing the properties of the cutter.
The use of a cutter to create perforations can be costly. In products that come pre-perforated, such as stamps, toilet paper, paper towels, etc., a large number of cutters must be used across a large web of material to provide a high throughput rate. These cutters must be serviced or often replaced when they become worn out. Additionally, the wear on the cutters leads to variations in the perforation size and depth so that operating parameters must be changed constantly to provide a uniform product.
In products that are simultaneously perforated and torn by a user, such as tape, aluminum foil, plastic wrap, etc., a metal cutter must either be provided with the product or acquired separately. This results in extra cost to the manufacturer or the user.
One way to overcome the problems of traditional cutting devices is to perforate material using lasers. Conventional laser methods produce perforations by forming a series of holes across the material. One advantage of using lasers to perforate material is that the laser vaporizes a small, well-defined point, rather than puncture or tear the material as with typical mechanical perforation machines. The use of lasers, however, still has a number of disadvantages.
It has been found that small holes are more efficient for perforations, because larger holes will not tear easily enough. Smaller holes, however mean a smaller operating area or “field size” because beam diameter is proportionate to the laser's field size. For example, a laser having a four inch field size is capable of creating holes having a diameter of about 0.02 mm. Though this hole size may be ideal for perforating certain materials, a web of material that is sixty inches across will require fifteen separate lasers in synchronized operation to successfully create the desired perforations.
Numerous problems exist in using multiple lasers to perforate material. The more lasers that are used the more complex a system becomes, requiring control and oversight for each unit. The lasers have to be perfectly synchronized in order to produce matching perforations. Considering no two lasers are identical in energy output, each laser has to be carefully calibrated and adjusted to perform in synchronization or inconsistencies will be obvious from one laser to another, and therefore in the perforations across the material. A malfunction or variation in any of the lasers would render the product unusable and require an entire production shutdown for maintenance.
An alternative to multiple lasers involves using beam splitters to produce separate beams from a single laser. There is a limit to the amount a laser beam can be split and remain effective so that more than one laser would still be required, providing the same problems as before but compounded by the further complexity of the beam splitter. Additionally, systems using split laser beams can be more costly than traditional ones.
In addition to the above mentioned deficiencies, typical laser perforation systems require a variety of complex process information. The hole size, hole shape, hole spacing, and hole amount must be controlled depending on the material in order to produce a product that is easy to tear. When multiple lasers must be used, each must have its own dedicated control system and the processing information must be entered and precisely implemented for each laser.